Generally, the angular velocity sensing devices for detecting the angular velocities of inertial bodies have been widely employed as a component of navigation apparatus in the ocean vessels, air planes and the like. At the present, this device has been extended to the navigation apparatus of automobiles, and to the high performance video cameras as a hand-oscillation compensating device.
The conventional gyroscope which has been used for military purposes and for air planes is manufactured by using a plurality of high precision components and through a complicated assembling process, and therefore, a precise performance is possible. However, its manufacturing cost is high, and its bulk is very large, with the result that it cannot be used for the general industries, and for the home power appliances.
Recently, a small gyroscope has been developed by attaching a piezoelectric device to a triangular prism beam, and this is used as a hand-oscillation sensor for a small video camera. Further, in order to overcome the difficulties of the gyroscope having the piezoelectric device, a small gyroscope with an improved cylindrical beam structure has been developed.
However, these two kinds of the small gyroscopes require precisely machined components, and therefore, the manufacture becomes difficult, while the manufacturing cost becomes high. Further, the mentioned two kinds of gyroscope includes a plurality of mechanical components, and therefore, it is difficult to form a circuit integration.
The principle of the gyroscope is as follows. That is, when a rotating inertial body which rotates or oscillates in a first axis direction receives an input of an angular velocity in a second axis direction (which is perpendicular to the first axis direction), the gyroscope detects a Coriolis force which acts in a third axis direction (which is rectangular to the first and second axes direction).
Under this condition, if the forces acting on the inertial body are made to be balanced, then the detection of the angular velocity has to be more precise. Particularly, if the linearity and the band width are to be expanded, a force balancing structure is required.
A conventional microgyroscope related to this technique is illustrated in FIG. 1.
As shown in FIG. 1, the microgyroscope includes: a plurality of combs 20 installed within a frame 10 in the lateral direction and in the sensing direction (y axis direction); a plurality of sensing direction (y axis direction) sensing electrodes 40 interposed between the combs 20, the electrodes 40 being supported by positive and negative electrode supporting parts 30 and 30'; sensing direction elastic bodies 50 installed at four places (the top and bottom and left and right) of the frame 10; oscillation structures 60 installed on the sensing direction elastic bodies 50 in the exciting direction (x axis); comb drivers 70 for causing oscillations on the oscillation structures 60 by supplying voltages; and exciting direction elastic bodies 80 disposed at the four corners of the oscillations structure.
In the conventional microgyroscope constituted as described above, the oscillation structures 60 are oscillated in the exciting direction (x axis) by receiving an ac voltage from the exciting drivers 70. When the oscillation structures 60 are oscillated, if an angular velocity input is received in a direction (y axis) perpendicular to the plane of the gyroscope, then a Coriolis force is generated in the sensing direction, with the result that the internal structures of the frame 10 are moved in the sensing direction. This movement causes a variation of the capacitance between the sensing electrodes 40 and the combs 20. Thus the amount of the angular velocity can be calculated by measuring the varied capacitance.
In the above described case, the oscillations caused by the influence of the oscillation structures 60 and the internal structures of the frame 10 can be reduced by separating the elastic exciting bodies 80 and the sensing direction elastic bodies 50 of the frame 10 of the gyroscope from each other by making them symmetric. However, there is a problem as described below. That is, the upper and lower portions of the oscillation structures 60 are installed on the sensing direction elastic bodies 50, and therefore, the upper portion and the lower portion of the oscillation structures make unstable movements up and down respectively.
Particularly, if the oscillation structures 60 and the frame 10 are to make stable oscillations in the exciting direction (x axis), there is required an element for sensing the oscillations of the oscillation structures. The oscillation signals which are detected by the oscillation sensing element supply certain exciting signals through a control circuit (which includes an external sensing circuit and an amplifying circuit) to the comb drivers 70. The oscillation structures 60 and the frame 10 perform stable oscillations at a resonance frequency which is decided by the mass of the oscillation structures 60, and the mass of the frame 10, and by the value of the exciting direction elastic bodies.
FIGS. 2A and 2B are graphical illustrations showing the ac signal interference by the exciting voltage supplied to both sides of the exciting comb drivers 70. As shown in these drawings, a negative interference effect is invited to the oscillation signals of the oscillation detecting element. Accordingly, stable oscillations become impossible.